Fine Structure and Olfactory Reception of the Labial Palps of Spodoptera frugiperda

The olfactory system of insects is essential in many crucial behaviors, such as host seeking, mate recognition, and locating oviposition sites. Lepidopteran moths possess two main olfactory organs, including antennae and labial palps. Compared to antennae, the labial palps are relatively specific and worthy of further investigation due to the labial-palp pit organ (LPO), which contains a large number of sensilla located on the tip segment. The fall armyworm, Spodoptera frugiperda, is a worldwide lepidopteran pest, which can damage more than 350 plants and cause significant economic losses. In this study, we surveyed the structure of the labial palps and LPO of S. frugiperda using a super-high magnification lens zoom 3D microscope. Then, the distribution and fine structure of sensilla located in the LPO of S. frugiperda were investigated using scanning electron microscopy. Subsequently, the electrophysiological responses of labial palps to CO2 and 29 plant volatiles were recorded by using electrolabialpalpography. Our results showed the fine structure of labial palps, the LPO, and the sensilla located in the LPO of S. frugiperda. Moreover, we demonstrated that the labial palps are olfactory organs that respond to both CO2 and other volatile compounds. Our work established a foundation for further study of the roles of labial palps in insect olfactory related behaviors. Further investigations on the function of labial palps and their biological roles together with CO2 and volatile compound responses in S. frugiperda are necessary, as they may provide better insect behavioral regulators for controlling this pest.

Transcriptome Characterization and Expression Analysis of Chemosensory Genes in Chilo sacchariphagus (Lepidoptera Crambidae), a Key Pest of Sugarcane

Insect chemoreception involves many families of genes, including odourant/pheromone binding proteins (OBP/PBPs), chemosensory proteins (CSPs), odourant receptors (ORs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs), which play irreplaceable roles in mediating insect behaviors such as host location, foraging, mating, oviposition, and avoidance of danger. However, little is known about the molecular mechanism of olfactory reception in Chilo sacchariphagus, which is a major pest of sugarcane. A set of 72 candidate chemosensory genes, including 31 OBPs/PBPs, 15 CSPs, 11 ORs, 13 IRs, and two SNMPs, were identified in four transcriptomes from different tissues and genders of C. sacchariphagus. Phylogenetic analysis was conducted on gene families and paralogs from other model insect species. Quantitative real-time PCR (qRT-PCR) showed that most of these chemosensory genes exhibited antennae-biased expression, but some had high expression in bodies. Most of the identified chemosensory genes were likely involved in chemoreception. This study provides a molecular foundation for the function of chemosensory proteins, and an opportunity for understanding how C. sacchariphagus behaviors are mediated via chemical cues. This research might facilitate the discovery of novel strategies for pest management in agricultural ecosystems.

Effects of urea on the olfactory reception in zebrafish (Danio rerio)

The effects of uremia on human olfactory functions have been clinically evaluated in various studies, even if to date it is not completely clarified which uremic toxins mediate these processes. Surprisingly, the role of the main molecule involved in uremia, urea indeed, has not been adequately investigated as other possible molecules may also be involved in uremic anosmia. The effects of urea on the olfaction have been evaluated in some clinical studies, but this is the first attempt to determine a direct action of urea on the olfactory epithelium of a vertebrate. <em>Danio rerio</em> adults were exposed to urea in different experiments to assess the effects on olfactory sensitivity and signal transduction. The analysis of the swimming speed has been used to evaluate the response to hypoxanthine 3-N-oxide (H3NO), a molecule that is known to elicit an olfactory-mediated alarm reaction in <em>D. rerio</em>. The presence and distribution of the G protein alpha subunit coupled to the olfactory receptors (Gα_olf) has been immunohistochemically investigated in the olfactory epithelium of control and urea-exposed <em>D. rerio</em>. Our findings showed that urea alters the response to H3NO of <em>D. rerio</em> with a quite rapid and reversible effect that appears to be independent from a mere interference of urea on the receptor-ligand binding. The Gα_olf protein resulted increases after urea treatment, suggesting an effect of urea on its expression or degradation.